wgpu does not honor platform alignment requirements on texture-buffer copies when they are stricter than WebGPU #7946
Description
As @cwfitzgerald noted in #6827, Metal specifies a "Buffer alignment for copying an existing texture to a
buffer" of 16B. WebGPU does not have this restriction. WebGPU's validating texture buffer copy only requires that the offset is aligned to a multiple of the block copy size, or in the case of depth/stencil, to 4B.
There are also failures of the offset_and_bytesPerRow and depth_stencil_format,copy_buffer_offset tests on dx12 that I haven't investigated, but I suspect may be a similar issue. Some of these may be fixed by #7721.
I noticed this while working on #7936, but I don't know if the CTS test in that issue (api,validation,image_copy,buffer_texture_copies:offset_and_bytesPerRow) will reliably catch issues here, since it's only checking the WebGPU requirements. It will only find violations of platform requirements if the violation actually occurs, if it results in a functional difference under the conditions of the test, and if the test is checking for functional correctness and not just correct validation.